Naruhito Sawanobori

Long lasting phosphorescence properties of Tb-activated reduced calcium aluminate glasses

A long lasting green phosphorescence was found in -doped calcium aluminate glasses prepared under a strongly reducing atmosphere. An electron-trapped centre giving an EPR signal at g = 1.999, an analogue of the centre in CaO, was induced by illumination with ultraviolet (uv) radiation and decayed slowly after the illumination was stopped. A partial oxidation of ions to ions by uv illumination was observed. A mechanism of the long lasting phosphorescence was suggested to consist of recombination of an electron released thermally from the -like centre with the photo-oxidized .

Long luminescent glass: Tb3+-activated ZnO–B2O–SiO2 glass

Abstract It has been found that zinc borosilicate glasses 60ZnO–20B 2 O 3 –20SiO 2 doped with 0.2 mol% Tb 2 O 3 exhibit phosphorescence after exciting with 254 nm light. This phosphorescence arises from f–f transitions of Tb 3+ ions and is observable by the eye, in the dark for up to 1 h after stopping the UV-illumination. Electron spin resonance (ESR) measurements show that electron trapping centers, associated with Zn ions, are formed by the UV irradiation and the phosphorescent centers decay after the irradiation was stopped. We suggest that this UV induced center is the photo-induced electron trap, which serves effectively as an electron donor, in the dark.

Formation of fluoride glasses based on AlF3YF3PbF2 system

Abstract A glass-forming region has been studied in the system of AlF3YF3PbF2. Colorless glasses, about 1 mm thick, have been prepared by quenching melts on a carbon plate. Upon replacing PbF2 by RF2, where R = Mg, Ca, Ba, or replacing YF3 by YbF3 in the ternary system, the glass thermal stability against crystallization is improved. Glasses with optimized composition are more stable than the well known AlF3YF3CaF2BaF2 glasses, and rods or disks have been prepared. The AlF3YF3PbF2-based fluoride glasses are characterized by a wide transmission window and higher chemical durability and mechanical strength than those in the ZrF4 system, and therefore are very promising for fiber or laser window material applications in the mid-infrared region.

Visible light emission and control by infrared-responsive materials

Upconversion characteristics of rare-earth cations were utilized for emitting or controlling visible light with infrared light. A fluorescent glass rod was fabricated by using durable AlF3-based glass that contained high-concentration Er3+ cations. This glass rod acted as a two-way wavelength converter; i.e., visible light (~500 nm) was converted to infrared light (~800 nm) as it passed through the glass, and infrared light that propagated in the opposite direction was converted to visible light. An infrared-responsive photochromic compound was fabricated by dispersing spirobenzopyran and upconversion powder (Gd2O2S:Yb3+Er 3+) in photocurable acrylate. When this compound was exposed to ultraviolet light (~370 nm), a strong absorption band appeared in the visible spectral region due to photochromic isomerization of spirobenzopyran. This absorption band disappeared by irradiation of a 940-nm laser beam, since the upconversion powder emitted green light that caused bleaching of colored spirobenzopyran.